1. Field of the Invention
The present invention relates to a wobble information detection method and system, for operation on a wobble signal output from an optical disc. In particular, the present invention relates to a wobble information detection method and system for detecting address information that has been encoded with minimum shift keying (MSK) and harmonic modulated wave (HMW) modulations, used for Blu-ray disc (BD), and/or with bi-phase (BP) modulation used in DVD formats, e.g., high definition digital versatile disc (HD-DVD) and digital versatile disc recordable and rewritable (DVD+R/RW) formats.
2. Description of Related Art
A conventional multi-format-compatible optical disc system includes an optical disc, an optical disc motor that rotates the optical disc, servo drivers that control the speed of the disc motor, and an optical pickup unit (OPU) that senses wobble information stored on the optical disc and generates a signal in response thereto. Since modulation of wobble signals for BDs is different from that for DVDs, the OPU can be used to sense differently encoded wobble signals on an optical disc.
Wobble signals sensed by the OPU are analyzed as a low pass filtered wobble signal, which contains address in pre-groove (ADIP) information and a recovered wobble carrier signal, also known as monotone wobble. The DVD format employs BP modulation, and, thus, is conventionally decoded using an exclusive OR (EXOR). The BD format, however, employs two different types of wobble modulation, combining MSK modulation, which uses a ×1.5 multiple of the frequency of the carrier signal, and HMW modulation, which uses a second harmonic of the carrier signal. These modulation schemes are not as simple to decode as the phase modulation schemes of DVD formats.
MSK modulation is realized by replacing every three monotone wobbles with one MSK Mark (MM). An MM includes three nominal wobble length (NWL) wobbles having the following wobble pattern: cos(1.5ωt), −cos(ωt) and −cos(1.5ωt). Thus, the MSK modulation uses one type of waveform, and differences in waveform position supply the information.
The HMW modulation is defined as cos(ωt)±sin(2ωt), resulting in two characteristic sawtooth waveforms (STWs). The STW including −sin(2ωt) has edges that fall gently at the beginning of the cycle and rise steeply at the end of the cycle, while the STW including +sin(2ωt) has edges that fall steeply at the beginning of the cycle and rise gently at the end of the cycle.
Each BD ADIP unit includes fifty-six (56) wobbles. Each BP ADIP unit begins with a starting MM signal that serves as sync for the BP ADIP unit. The difference in position of a second and a third MM signal following the starting MM signal represents the type of ADIP unit. The ADIP address and sync is decoded by analyzing the detected MM data. Even though MSK modulation is more sensitive to phase shift noise, it provides accurate position information useful for sync, whereas HMW modulation provide more accurate data “0” and data “1” detection since the data “1” STW and data “0” STW signals are repeated 37 times.
Since there are 69 channel clock signals in one BD wobble cycle and HMW uses the second harmonic of the wobble clock, a second clock recovery circuit is needed to generate the second harmonic of the wobble. Thus, in order to perform analog synchronous detection of MM and STW, two sets of multipliers, integrators and clock recovery circuits are required. Such analog components consume large chip area and power.